By correlating known diabetes duration with the prevalence of retinopathy, more than 10 years have been estimated to lapse between the onset and diagnosis of type 2 diabetes. Such calculations, however, assumed a linear model, included stages of retinopathy not specific to diabetes, and allowed 5 years for retinopathy to occur after the onset of diabetes. We calculated the duration of undiagnosed type 2 diabetes in outpatients screened for retinopathy in a hospital-based diabetes clinic after correcting these assumptions.RESEARCH DESIGN AND METHODS
Diabetic patients (n = 12,074; 35,545 fundus examinations) were stratified into younger onset (YO; age at onset <30 years) or older onset (OO; age at onset ≥30 years), insulin treated (IT) or not IT (NIT), and with mild/more severe diabetic retinopathy (AnyDR) or moderate/more severe diabetic retinopathy (ModDR). The best-fitting equation correlating known duration among the OO-NIT group with the prevalence of ModDR was used to extrapolate time from appearance of retinopathy to diagnosis of type 2 diabetes. Time for retinopathy to develop after diabetes was calculated from the equation correlating the duration among the YO-IT group with appearance of ModDR.RESULTS
There were 1,719 patients in the OO-NIT group with AnyDR and 685 with ModDR and 756 in the YO-IT group with AnyDR and 385 with ModDR. A linear model showed ModDR appeared 2.66 years before diagnosis among those in the OO-NIT group. A quadratic model suggested that ModDR appeared 3.29 years after diagnosis among those in the YO-IT group. The resulting estimate was 6.05 years (2.66 + 3.29) between the onset and diagnosis of diabetes, compared with 13.36 years using standard criteria.CONCLUSIONS
Using best-fitting models and stratifying by glucose-lowering treatment and severity of retinopathy substantially lowers the estimated duration of undiagnosed type 2 diabetes.